1. Field of the Invention
The present invention relates to an optical grain sorter used to sort out grains (defective grains) not normal in external appearance as a grain product from grain distributed on the market. More particularly, the present invention relates to an optical grain sorter of this kind arranged so that an operator can adjust a level of determination sensitivity (a threshold value set in the optical grain sorter) provided in the sorter for sorting normal grains (grains having a normal external appearance) and defective grains from each other, by seeing a display on a display device provided on the sorter.
2. Description of Related Art
In distribution of grain on the market, the commodity value should be improved by removing defective grains not normal in external appearance as grains. To do so, an optical grain sorter is used. However, while a certain degree of sorting suffices for avoiding any problem in terms of commodity value, there is a possibility of inappropriate setting of the level of sorting in some case of use of an optical grain sorter, depending on the kind or grade of grain or on the degree of cleaning. In such a case, it is necessary for an operator of the sorter to adjust the degree of sorting with the sorter as desired while checking the state of sorting with the sorter.
FIG. 1 shows the principle of grain sorting adopted in a conventional optical grain sorter. The grain sorting shown in FIG. 1 is sorting of cleaned rice grains. According to the principle, a grain from which a signal level corresponding to 75% or less of the background signal level assumed to be 100% is detected with a CCD line sensor is recognized as a grain having a light colored portion; a grain from which a signal level corresponding to 50% or less of the background signal level is detected is recognized as a grain having a dark colored portion; and these grains are determined as defective grains.
In the grain having a light colored portion, the light colored portion occupies at least a certain area in the grain surface such that this grain is discriminable from normal grains, and the degree of coloring of the colored portion is low (the color is light). In the grain having a dark colored portion, the deep colored portion has such a color in the grain surface that this grain is discriminable from normal grains, and the degree of coloring of the colored portion is high (the color is dark). The grain having a dark colored portion comprises any grain having a dark colored portion regardless of the area of the dark colored portion. The grain having a light colored portion and the grain having a dark colored portion are defective grains collectively called “colored grain”.
In the conventional optical grain sorter, sorting of defective grains from normal grains is determination as to which drop in signal level from the signal level corresponding to normal grains with respect to the 100% background signal level indicates a defective grain. This is adjustment of a threshold value set in the optical grain sorter. Conventionally, the threshold value to be set is adjusted by seeing the actual state of sorting, displaying a signal from an optical sensor on an oscilloscope or touch panel monitor screen and seeing the signal.
An optical grain sorter described in Japanese Patent Laid-Open No. 2005-74412 displays on a monitor in an operating panel images of grains taken by image pickup means such as a CCD line sensor (binary data on the contours of grains), images of colored portions of grains having light colored portions (binary data on the shapes of the portions) and images of colored portions of grains having dark colored portions (binary data on the shapes of the portions). An operator of the sorter can determine whether or not defective grains are discriminated as expected by seeing the display on the monitor screen while seeing the actual state of sorting of grains.
The means adopted in the optical grain sorter described in Japanese Patent Laid-Open No. 2005-74412 has improved the trail-and-error condition in the conventional art using an oscilloscope when determination as to whether or not defective grains are discriminated as expected is required. That is, an operator of the optical grain sorter described in Japanese Patent Laid-Open No. 2005-74412 can directly grasp, as actual images of grains from a display on the monitor screen, the contours of grains and the sizes and shapes of colored portions in defective ones of the grains actually grasped by the optical grain sorter, instead of grasping them from a simple display of data on an oscilloscope. In this way, the facility with which a threshold value to be set in the optical grain sorter is set so that defective grains can be discriminated as expected is improved.
As a result, the operator can adjust the threshold value more efficiently in this sorter than in those previously proposed. Also, the accuracy of the threshold value is improved.
The means adopted in the optical grain sorter described in Japanese Patent Laid-Open No. 2005-74412 is excellent in that it enables an operator to adjust the threshold value for discrimination between normal grains and defective grains while seeing actual images of the grains on a monitor. However, it has a problem in terms of image display technique and, hence, the drawback of not facilitating discrimination between normal grains and defective grains displayed on the monitor. That is, the contours of a multiplicity of grains are displayed on one monitor screen, and colored portions of defective ones of the grains are displayed by being superposed on the contours of the grains, accompanied by their shapes and sizes. The images on the monitor are thus complicated, so that it is difficult to discriminate defective grains having light colored portions and defective grains having dark colored portions and there is a possibility of an operator failing to notice defective grains. It is necessary to unfailingly sort out defective grains having dark colored portions in particular. After the occurrence of failure to notice a defective grain having a dark colored portion and after the completion of sorting, the defective grain may be found in normal grains. Such an incident leads to a considerable reduction in reliability of the sorting process.
The technique for the optical grain sorter described in Japanese Patent Laid-Open No. 2005-74412 also has a problem that an operator is uncertain as to whether or not defective grains are correctly separated by air jet nozzles for separating defective grains from normal grains.